If you believe animals are inferior and should be treated as such:

"All the arguments to prove man's superiority cannot shatter this hard fact: in suffering, the animals are our equals."
-- Peter Singer

"The question is not, 'Can they reason?' nor 'Can they talk?' but 'Can they suffer?"
-- Jeremy Bentham

"The worst sin toward our fellow creatures is not to hate them, but to be indifferent to them. That is the essence of inhumanity"
-- George Bernard Shaw

"There is no religion without love, and people may talk as much as they like about their religion, but if it does not teach them to be good and kind to other animals as well as humans, it is all a sham."
-- Anna Sewell

If you blieve the slaughtering of animals is all good and fine:

"If you can justify killing to eat meat, you can justify the conditions of the ghetto. I cannot justify either one."
-- Dick Gregory

"The time will come when people such as I will look upon the murder of (other) animals as they now look upon the murder of human beings."
-- Leonardo Da Vinci

In hope for the nation, the world, and us as a race:

"The greatness of a nation and its moral progress can be measured by the way its animals are treated."
-- Mahatma Gandhi

"Until we establish a felt sense of kinship between our own species and those fellow mortals who share with us the sun and shadow of life on this agonized planet, there is no hope for other species, there is no hope for the environment, and there is no hope for ourselves."
-- Jon Wynne-Tyson

"If by some miracle in all our struggle the earth is spared from nuclear holocaust, only justice to every living thing will save humankind."
-- Alice Walker

If you believe the compassion taught in religion does not apply to animals:

"There is no religion without love, and people may talk as much as they like about their religion, but if it does not teach them to be good and kind to other animals as well as humans, it is all a sham."
-- Anna Sewell

About the relationship between human and animal, hardly seen yet:

"In the relations of humans with the animals, with the flowers, with all the objects of creation, there is a whole great ethic scarcely seen as yet."
-- Victor Hugo

Don't believe in Animal Rights? - the truth about truths:

"It is the fate of every truth to be an object of ridicule when it is first acclaimed."
-- Albert Schweitzer